Calcium lactate is a salt of a weak organic acid and is represented as `Ca(Lac)_2`. A saturated solution of `Ca(Lac)_2` contains 0.13 mol of this salt in 0.5 litre solution. The pOH of this solution is 5.6. Assuming complete dissociation of the salt, calculate `K_a` for latic acid.

Explanation

`Ca(Lac)_2(s) to Ca(Lac)_2 (aq) to Ca^(2+)(aq) + 2Lac^(-) (aq) `
`Lac^(-) (aq) + H_2O hArr LaCH(aq) + OH^(-) (aq)`
Since it is salt of strong base and weak acid, its pH is calculated as
pH=14-pOH=14-5.6=8.4
`8.4= 1/2[14+pK_a + log 0.52]` (`therefore` c = 2 × 0.13/0.5)
`pK_a`= (2 × 8.4) – 14 – log 0.52 = 3.08
`therefore K_a=8.31xx10^(-4)`